Geochemical analyses of bitumen and sediments from highly biodegraded oil sand samples presents substantial business and analytical challenges for routine characterization. Access to data from rapid, reliable characterization of oil sands bitumen and sediment is critical to daily operations and business decisions. Some laboratories may lack the capability or turn-around time to adequately provide data on a daily basis. The nature of the samples prevents the use of traditional mineralogical analyses, such as optical microscopy, x-ray diffraction, and x-ray fluorescence, until the sediments of interest are isolated from the bitumen in the sample. Conventional geochemical extraction techniques are limited by the high level of bitumen saturation in oil sands samples and the decreased solubility of the asphaltene-rich bitumen in traditional organic solvents, requiring substantial time and solvent volume requirements in order to provide quantities of extracted sediment suitable for characterization.
Standard geochemical extraction techniques, such as Soxhlet or Soxtec extractions, are limited in their extraction efficiency by the azeotropic boiling point of the solvent mixture under normal conditions. High levels of bitumen saturation (e.g., greater than 1%) in oil sand samples, combined with the decreased extraction efficiency of conventional techniques, can require substantial time (e.g., days to weeks) and solvent requirements (e.g., greater than 1 liter) in order to provide quantities of extracted sediment suitable for characterization (e.g., greater than 10 grams). Conventional extraction techniques typically lose clay minerals and fines (e.g., less than 10 μm) during the extraction process; this fraction of sediment is critical since fines content may be a controlling factor when determining overall bitumen extractability during mining processes. Access to data from this fraction will be critical in order to address daily operation and business-related decisions.
Prior publications have compared conventional solvent extraction techniques against microwave extraction techniques and have shown that microwave techniques typically utilize lower solvent volumes and reduced extraction times. For example, application of microwave technology at analytical-scale extractions were first proposed in the mid-1980's and showed comparable-to-improved recoveries relative to traditional analytical extraction techniques, although solvent choice was a strong driver for overall recovery of given compounds. See e.g., Ganzler, K., Salgo, A., Valko, K., “Microwave Extraction: A Novel Sample Preparation Method for Chromatography,” Journal of Chromatography, 371, 299-306 (1986). The largest advantage to microwave extraction techniques was understood to be the substantially-reduced solvent volumes (e.g., up to 100 times less) and reduced extraction times. Additional work included extraction of polycyclic aromatic compounds and hydrocarbons from source rocks, which showed 88-96% recovery of spiked rock samples compared to Soxhlet techniques, while extraction from natural rock samples showed increased extraction yields, from 86-119%, depending on compound type. See e.g., M Letellier, H Budzinski, J Bellocq, J Connan, “Focused microwave-assisted extraction of polycyclic aromatic hydrocarbons and alkanes from sediments and source rocks”, Organic Geochemistry 30, 1353-1365, ISSN 0146-6380 (November, 1999). More recent work has focused on the extraction of chlorinated pollutants from soils and tissues using microwave techniques relative to more traditional Soxhlet or accelerated solvent extraction techniques; in all cases microwave extractions were shown to have increased recoveries, shorter extraction times and lower solvent volumes when appropriate solvents (appropriate for what is being extracted) are utilized. See e.g., Wang, Pu; Zhang, Qinghua; Wang, Yawei; Wang, Thanh, et al., “Evaluation of Soxhlet Extraction, accelerated solvent extraction and microwave-assisted extraction for the determination of polychlorinated biphenyls and polybromnated diphenyl ethers in soil and fish samples,” Analytica Chimica Acta 683, 43-48 (2010). See also, Zhang, Peng, Linke, G E, Zhou, Chuanguang, et al., “Evaluating the performances of accelerated-solvent extraction, microwave-assisted extraction, and ultrasonic-assisted extraction for determining PCBs, HCH's and DDT's in sediments.” Chinese Journal of Oceanology and Limnology 29, No. 5, 1103-1112 (2011). Overall, the literature supports the proposition that, for the particular substances they were being applied to, microwave extraction provides overall increased extraction recoveries, efficiencies, and reduced solvent volumes without appreciable degradation of the compounds of interest. However, little work has focused on the direct analysis of petroleum hydrocarbons, in particular oil sands bitumen composition, using microwave extraction techniques.
The application of microwave technology to oil sand bitumen extractions was proposed as early as the late 1970's to 1980's, although these proposals focused on the upgrading of heavy oil sands bitumen to more refinable products. For example, a microwave heating system was utilized to yield up to 86% recovery of initial bitumen composition, with the remaining waste composed of 1-2% carbon graphite and various hydrocarbon gases, including hydrogen, acetylene, methane carbon monoxide, and carbon dioxide. See R. G. Bosisio, J. L. Cambon, C. Chavarie, D. Klvana, “Experimental results on the heating of Athabasca tar sand samples with microwave power,” Journal of Microwave Power 12 (4) 301-307 (1977). However, these experiments were performed in a solvent-free system and relied only on in-situ sample water for heating. U.S. Pat. No. 4,419,214 describes irradiated oil sands, shale rock, and lignite under pressure and utilized gaseous or liquid CO2 and/or other vapor hydrocarbon solvents in high frequency microwaves. Canadian Patent Nos. 1,293,943 and 1,308,378 utilized aqueous solvents to show separation of oil sand bitumen from mineral phases at both elevated (e.g., 500° C.) and low (e.g, less than 100° C.) temperatures. However, these Canadian patents describe bitumen separation into an upper bitumen fraction and a lower mineral fraction, describing each layer merely as containing a greater proportion of either bitumen or mineral than the other layer. A series of experiments in U.S. Pat. No. 4,419,214 suggest that anywhere from 20% to over 90% of tar was removed from mineral sands during the process.
More recent work in the past decade has again focused on technologies and methods that utilize microwave energy to both increase heavy oil production and to degrade heavy oils to more refinable products. For example, U.S. Patent Application Publication No. 2007/0137852 proposed a technology that would extract hydrocarbon fuel products like kerogen oil and/or gas from solid hydrocarbon using a combination of electrical energy that was provided by an electromagnetic field generator to critically heat CO2, N2O or O2 in subsurface heavy oil accumulations, producing a less viscous vapor, liquid, or dissolved oil phase that would be pumped back to the surface. Similar techniques disclosed in U.S. Patent Application Publication Nos. 2009/0139716 and 2011/0253362 suggest using microwave energy to help mobilize subsurface accumulations of heavy oil, either by direct heating using field-wide wells with electromagnetic heating (as in U.S. Patent Application No. 2009/0139716) or by using microwave energy to heat production water pumped into subsurface reservoirs (as in U.S. Patent Application No. 2011/0253362) with the goal of, in both cases, reducing oil viscosity to increase hydrocarbon recovery. U.S. Pat. No. 7,629,497 has suggested development of large-scale microwave technologies that would degrade petroleum-containing compounds such as tires, plastics, etc. or that could be used for the recovery of subsurface heavy oils, oil shales, or tar sands. U.S. Patent Application No. 2011/0114470 describes a technique for application at surface mine sites, where microwave energy is used to dry and refine hydrocarbons to a more refinable state, with bitumen recoveries that range from 50-80%.
Despite the amount of research into microwave technology in the separation of oil sands, these separation recoveries using these techniques have only been qualitatively reported and are unlikely to be robust enough for geochemical or mineralogical characterization of the resulting bitumen or mineralogy despite extensive analytical research in other fields that suggests microwave extractions may be more robust than traditional extraction techniques. Therefore, there remains a need for reliable and relevant sample preparation methods to address questions related to daily mining operations, such as analytical extraction technique for oil sands.